When organic molecules are used in memory cells, the memory cells can be made smaller in size, because organic molecules themselves are small in size. As a result, storage density of memory using molecules can be increased The operation of memory cell can be achieving the change between the low resistance state and the high resistance state, and the change is corresponding to the change of electric current. For this purpose, molecules having a function to change its resistance depending on the applied electric field or injected charges are introduced between upper and lower electrodes. To change the state, the voltage is applied between the upper and lower electrodes The difference of state can be detected by the electric current. In this manner, a memory cell is formed. In this manner, a memory cell is formed. Another operation of memory cell can be achieving the change of the stored charges in molecule between the channel (electrode) and the gate electrode of FET, and the change is corresponding to the change of drain current. For this purpose, molecules having a function to storing injected charges are formed on an electrode, and the charges injected from the electrode are stored in the molecule. To change the stored charges, the voltage is applied between the upper and lower electrodes. The charge-stored state can be detected by the drain current. Such attempts have also been made to form memory cells. Alternatively, molecules having a function to store injected charges are formed on an electrode, and the charges injected from the electrode are stored. The charge-stored state is read out. In this manner, a memory cell is formed.
In a small memory cell, the distances between the charges in the molecules and the surrounding electrodes are short. Therefore, charges are easily cleared from molecules due to movement of charges between the molecules and the electrodes. As a result, the charge retention time (the data retention time or life) of the organic molecular memory becomes shorter.